The invention relates to a method for electro-optical distance measurement. The invention further relates to a device for carrying out the method.
EP 0,312,524 B1 discloses a method for electro-optical distance measurement according to the pulse time-of-flight method, in which individual radiation pulses are transmitted periodically by a transmitter and detected as echo signals by a receiver. The detected radiation pulse signals are sampled, digitized, added period-fashion in an adder and then stored in a memory. A memory location of the memory is respectively assigned for the sampling values of a period. At the start of each transmission of a radiation pulse signal, the sampling values of the detected radiation pulse signals are added to the already-stored sampling values of the radiation pulse signals detected in the previous period. With an increasing number of measurements, the addition of the sampling values leads to the formation of a sum pulse signal, from the time position of which in relation to the time of the pulse transmission, the time of flight of the radiation pulse signal can be determined. A disadvantage of this method is that a high sampling rate is required in order to ascertain the precise position of the echo signal. Since the sampling rate is limited for technical reasons, and, in addition, a higher sampling rate requires a larger memory, only a particular number of sampling values per impulse signal are available for evaluation. As a result, errors may occur when the time position of the detected pulse signal is determined, especially if the shape of the pulse signal is altered by external effects.
In addition, DE 40 31 668 A1 discloses a method for electro-optical distance measurement, in which a sequence of individual light pulses is transmitted periodically. The signal transmitted as a pulse sequence is a spread-band signal, so that the duration of the transmitted signal is substantially greater than the reciprocal spectral bandwidth thereof. After a pulse sequence has been transmitted, the next pulse sequence is transmitted, the detected light signals being added with the period of the pulse sequence and stored. In order to determine the time of flight, the transmitted pulse sequences need to be reflected on two measurement objects. The two times of flight of the pulse sequences are approximated by using a maximum likelihood algorithm, so that the distance can be determined by ascertaining the difference in time of flight. A disadvantage with this known method is that transmitters, in particular pulse laser diodes with about 1000-fold greater peak power and comparable average power to CW laser diodes, cannot be used. Since, with pulse laser diodes, a comparatively large time must be waited before the next pulse is transmitted, it is not possible to transmit a spread-band signal.